1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a sheet fed from a sheet storing unit, and, more specifically, to the stiffness of a frame member of an image forming apparatus.
2. Description of the Related Art
Up to now, an image forming apparatus (hereinafter, referred to as a main body) of a copying machine, a printer, a fax machine and combined machines of these machines includes a sheet storing unit, an image forming unit, a fixing unit, a sheet feeding unit and a sheet discharging unit. The sheet storing unit has a bundle of sheets placed therein, and the sheets are recording materials such as plain paper. The sheet feeding unit separates and feeds the sheets one by one from the bundle of sheets in the sheet storing unit, and conveys the sheets toward the image forming unit. The image forming unit forms an image on a sheet. In the case where an electrophotography method is applied to the image forming unit, a toner image that is formed on a sheet by the image forming unit is heated and pressurized on the sheet by the fixing unit. A sheet on which an image is recorded is discharged by the sheet discharging unit. Each of these units is fixed to a frame unit that functions as the skeleton structure of the main body directly or with the intermediation of some members. Among these units, the sheet storing unit is a universal cassette attachable and detachable with respect to the main body in many cases, in order to facilitate refilling with a bundle of sheets. The sheet feeding unit is fixed to the main body, and includes a feeder that separates and feeds a sheet from the bundle of sheets on the universal cassette, in many cases. The universal cassette is mainly provided to a lower portion of the main body in many cases.
In general, in order not to impair the image quality of the image forming apparatus, the amount of change in relative position of each of the above-mentioned units is reduced by enhancing the stiffness of the frame member. The frame member normally has one of a box-like shape and a shape equivalent thereto. Mainly with regard to the bottom surface of the main body, for example, Japanese Patent Application Laid-Open No. 2008-90042 discloses a large-size image forming apparatus including a bottom plate that is a substantially plate-like member and entirely covers the bottom surface of the main body. The use of a small member such as a stay and a configuration in which the bottom surface is opened are known for middle-size and small-size image forming apparatuses.
Unfortunately, if the bottom plate is used for the bottom surface of the main body as described above, the size of the main body, particularly, the size thereof in the height direction becomes larger depending on the shape of the bottom plate, in the case of, for example, such a large-size main body as disclosed in Japanese Patent Application Laid-Open No. 2008-90042.
In a configuration known for a small-size main body, any of the image forming unit, the fixing unit and the sheet discharging unit is provided with a function as a reinforcing member for the main body, whereby the bottom plate is omitted. Because the bottom plate is omitted in such a configuration, a cost corresponding to the bottom plate does not occur. Unfortunately, from the perspective of strength, particularly, strength necessary to transport the main body, there is a limit on the distance between the bottom surface and any of the units that is used as the reinforcing member as an alternative to the bottom plate. Hence, the main body that can have such a configuration is limited to a small apparatus. Further, from the perspective of a reduction in environmental load concerning the amount of used material and product weight, a reduction in thickness of plates used to form the frame member is being required. Under the circumstances, when the main body is transported, the frame is highly likely to deform due to palletization of the main body in a packaged state and an impact caused by dropping, and hence omission of the bottom plate is becoming difficult.
A conceivable method for solving this includes using a packaging material that protects the frame member and prevents deformation thereof, only during transportation. However, the size of the packaging material becomes larger for the purpose of protecting the frame member, so that an environmental load increases.
In view of the above, the present invention proposes a sheet stacking apparatus in which: a sheet storing unit serves as a strengthening member for a frame member in the state where the sheet storing unit is inserted in the frame; and strength necessary to, for example, transport a main body of the apparatus is thus secured with a low environmental load and at low costs.